1. Field of the Invention
The present invention relates to a photographic lens system which has a wide photographing field angle of approximately 64.degree., a small F number on the order of 2.8, a telephoto ratio of approximately 1.1 or lower, a compact size, optical performance scarecely degraded within a photographing range from infinite distance to a short distance on the order of 0.35 m, and provides images of high qualities.
2. Description of the Prior Art
In recent years, image pickup lens systems used in photographing silver salt cameras and still video cameras have been configured mainly as zoom lens systems which can conveniently cope with various photographing conditions. However, zoom lens systems hardly have total lengths as short as those of lens systems having fixed focal points, tend to have small F numbers at tele positions in particular when they are configured to be compact, and cannot form images of satisfactory qualities.
Accordingly, users desire pocketably compact and cute cameras more and more strongly and more compact cameras that use bright lens systems with fixed focal points that form images of high quality.
There are conventionally known photographic lens systems, each of which are composed of four lens components of four lens elements, like the lens system according to the present invention. For example, a lens system disclosed by Japanese Patent Kokai Publication No. Sho 55-73014 is composed of four lens components of four lens elements. However, these conventional photographic lens systems are dark, or have F numbers on the order of 3.5 to 5.6, and cannot sufficiently satisfy the users' recent desire for shorter minimum photographing distances, or exhibit favorable optical performance at their minimum photographing distances.
Further, a lens system disclosed by Japanese Patent Kokai Publication No. Sho 57-116313 has a composition similar to that of the photographic lens system according to the present invention and a small F number of F2.8, but allows an amount of marginal rays to be reduced by stopping down, thereby producing a phenomenon that four corners of a film are darkened in the stop down condition. In addition, the conventional lens system allows aberrations to be varied remarkably from infinite object distance to a short object distance and cannot provide photographs desired by users when it is used for photographing objects located at extremely short distances in particular.
For configuring a compact camera using a photographic lens system having a fixed focal point so as to satisfy the users' desire for photographing objects located at a minimum photographing distance, it is necessary to design the lens system to permit photographing an object located an extremely short distance (on the order of 0.35 m).